1. Field of the Invention
The present invention relates to a wire-cut electric discharge machine and in particular to a method of and a device for adjusting perpendicularity of a wire with respect to a reference plane on which a workpiece is mounted.
2. Description of Related Art
The wire-cut electric discharge machine performs electric discharge machining by feeding a wire to extend between a pair of wire guides and exerting an electric voltage between the wire and a workpiece arranged between the pair of wire guides. There are known wire-cut electric discharge machines of a vertical type and a horizontal type. In the vertical-type wire-cut electric discharge machine, as shown in FIG. 12, an upper wire guide 5a and a lower wire guide 5b are arranged vertically (in a Z-axis direction) for guiding a wire 6 to extend therebetween. A workpiece mounting table 4 for mounting a workpiece W is arranged between the upper guide 5a and the lower guide 5b. The mounting table 4 is driven in a X-axis direction and a Y-axis direction perpendicular to each other on a horizontal plane. The mounting table 4 has a Y-axis unit 4y arranged on a base 1 and driven in the Y-axis direction by a Y-axis servomotor My and a X-axis unit 4x arranged on the Y-axis unit 4y and driven in the X-axis direction by an X-axis servomotor Mx. A workpiece W is mounted on a workpiece mounting member 4c fixed on the X-axis unit 4x. The electric discharge machining is performed by exerting a machining voltage between the wire 6 and the workpiece W while moving the workpiece W mounted on the mounting table 4 by driving the X-axis servomotor Mx and the Y-axis servomotor My. Further, one of the wire guides 5a and 5b is arranged movable in directions of two rectangular axes for performing a tapered machining, etc. on the workpiece W.
In the example of FIG. 12, the lower wire guide 5b is fixed at a distal end of a horizontal beam 3 extending from a column 2 provided vertically on the base, and the upper wire guide 5a is arranged on a horizontal beam (not shown) extending from the column 2 and driven in directions of a U-axis and a V-axis perpendicular to each other by a U-axis servomotor and a V-axis servomotor (not shown), respectively. It is usual that the U-axis is arranged parallel to the X-axis and the U-axis is arranged parallel to the Y-axis. In the following description, a plane defined by the X-axis and the Y-axis is referred to as a reference plane.
In the horizontal type wire-cut electric discharge machine, as shown in FIG. 13, a pair of heft-hand and right-hand wire guides 5L and 5R are arranged horizontally (in a Z-axis direction) and a wire 6 is arranged to extend between the heft-hand wire guide 5L and the right-hand wire guide 5R. A workpiece mounting table 4 for mounting a workpiece W thereon is arranged between the light-hand wire guide 5L and the right-hand wire guide 5R. The electric discharge machining is performed by exerting a machining voltage between the wire 6 and the workpiece W while moving the workpiece W on a vertical reference plane in the X-axis direction and the Y-axis direction by driving the X-axis servomotor and the Y-axis servomotor (not shown).
Further, in FIG. 13, in order to perform a tapered machining, etc,, one of the wire guides 5L and 5R has driving means for driving the wire guide in directions of two rectangular axes (usually parallel to the X-axis and the Y-axis, respectively) on a plane parallel to the vertical reference plane. In the example of FIG. 13, the left-hand wire guide 5L is driven in U-axis and V-axis directions respectively parallel to the X-axis and the Y-axis by the U-axis and V-axis servomotors (not shown).
In the above described wire-cut electric discharge machines having means for driving one of the wire guides in directions of two rectangular axes, it is necessary to obtain positions of the wire guides in a U-V coordinate system for guiding the wire 6 to extend precisely perpendicular to the reference plane.
There is known, from Japanese Patent No. 2698664, a device for adjusting perpendicularity of the wire by controlling a direction of the wire so that the wire is brought into contact with a pair of contact pieces, which are arranged in a direction perpendicular to the reference plane, simultaneously and at the same positions on the pair of contact pieces.
Further, there is disclosed, in Japanese Patent No. 2752550, an apparatus for obtaining an angle of the wire based on a displacement of positions of the wire respectively in contact with a pair of contact pieces arranged to be horizontally and vertically displaced on a vertical plane.
As the wire guide for guiding the wire, a dice-like guide which has a though hole forming a gap of 5 xcexcm-20 xcexcm between an inner circumference thereof and an outer circumference of the wire is generally used. Specifically, as shown in FIG. 1, a gap xcex1 of 5 xcexcm-20 xcexcm is formed between an inner circumference of the through hole of the wire guides 5 and the outer circumference of the wire 6. Therefore, when the wire 6 extending between the pair of wire guides aligned to be perpendicular to the reference plane is brought into contact with the contact piece, the wire moves in a range of the gap in the through hole to make an error in adjusting the perpendicularity of the wire. Thus, a precision of the adjustment can not be improved to a degree less than the gap xcex1 in the wire guide according to the above methods in which the wire extending between the wire guides aligned to be perpendicular to the reference plane is brought into contact with the contact piece for compensating an error of perpendicularity of the wire based on the contact positions of the wire with the contact piece.
Further, the method in which the wire is simultaneously brought into contact with the pair of contact pieces has a problem in that detection means such as a detection circuits for detecting a contact between the wire and the contact piece is necessary for each of the pair of contact pieces.
An object of the present invention is to provide a method of and a device for adjusting perpendicularity of a wire of a wire-cut electric discharge machine capable of performing higher precision machining with low cost.
A method of adjusting perpendicularity of a wire of the present invention is applicable to a wire-cut electric discharge machine of the present invention having a driving mechanism for driving a workpiece mounting table in direction of two rectangular axes defining a reference plane, a pair of wire guides for guiding a wire perpendicularly to the reference plane, a driving unit for driving one of the wire guides on a plane parallel to the reference plane. The method comprises the steps of:
(a) arranging an adjusting jig having at least one pair of contact pieces spaced apart from each other on a reference perpendicular plane perpendicular to the reference plane, on the workpiece mounting table;
(b) moving said one of the wire guide so that the wire is inclined in a direction other than a direction perpendicular to the reference perpendicular plane to enable the wire to come into contact with only one of the pair of contact pieces;
(c) moving the adjusting jig so that the wire comes in contact with only said one of the pair of contact pieces and obtaining a first contact position of the wire in contact with said one of the pair of contact pieces;
(d) moving the adjusting jig to enable the wire to come into contact with the other of the pair of the contact pieces;
(e) moving the adjusting jig so that the wire comes into contact with only the other of the pair of contact pieces and obtain a second contact position of the wire in contact with the other of the pair of contact pieces;
(f) obtaining a displacement amount of said one of the wire guides with respect to the reference perpendicular plane based on a difference between the first contact position and the second contact position;
(g) moving said one of the wire guides in a direction to compensate the obtained displacement amount to adjust perpendicularity of the wire on a plane parallel to the reference perpendicular plane;
(h) performing the steps (b)-(g) with respect to another reference perpendicular plane perpendicular to the reference plane to adjust perpendicularity of the wire on a plane parallel to said another reference perpendicular plane.
The steps (b)-(g) may be repeatedly performed until the difference between the first contact position and the second contact position is not greater than a predetermined value or the displacement amount of said one of the wire guides is not greater than a predetermined amount.
The wire may be inclined on a plane parallel to the reference perpendicular plane in the step (b).
The reference perpendicular plane may be parallel to one of the two rectangular axes of the driving mechanism for driving the workpiece mounting table.
The driving unit may drive said one of the wire guides in two directions respectively parallel to the two rectangular axes of the driving mechanism for driving the workpiece mounting table.
The contact piece of the adjusting jig may have a portion in the form of a plane, a generatrix line of a cylinder or a semi-cylinder, or a ridge line for contact wit the wire, and lines respectively connecting points of contact of the pair of contact pieces with the wire are parallel to each other or extensions of the lines intersect with each other at an acute angle.
The contact between the wire and the adjusting jig may be detected by a workpiece end face detection circuit for detecting a contact between the wire and a workpiece.
The adjusting jig may be made of electrically conductive material to equalize electric potential at whole portions thereof.
A positional error of the pair of contact pieces of the adjusting jig with respect to the reference perpendicular plane may be measured and stored in advance and the displacement amount of said one of the wire guides may be compensated using the stored positional error.
The adjusting jig may be made of electrically conductive material having corrosion resistance against machining fluid.
A block having side faces perpendicular to the reference plane when mounted on the workpiece mounting table may be used as the adjusting jig. In this case, an upper portion and a lower portion of the block are used as the pair of contact pieces.
The present invention also provides a device for carrying out the above method of adjusting perpendicularity of a wire of a wire-cut electric discharge machine.